We will continue our investigations on the structure, mechanism and biological functions of the three citrate enzymes, citrate lyase, citrate synthase and ATP-citrate lyase. In this proposal we intend to examine the structure of citrate synthase in situ in relation to the change in its inhibitory pattern from an ATP sensitive enzyme in vitro to an ATP insensitive one in vivo. We shall also attempt to determine if the genes for citrate lyase are carried by a plasmid and attempt to isolate and study these genes. Finally, we shall study the residues and surrounding peptides in ATP-citrate lyase that are responsible for the formation of a histidyl phosphate intermediate and the citryl enzyme intermediate in the overall reaction. We will study the properties of the recently purified rat brain ATP-citrate lyase. We will continue our efforts to relate the mechanisms and structures of the three citrate enzymes. In addition, we will use the information on enzyme structure and mechanism to gain insight into each enzymes biological role and the control of its activity.